Surface treatment method for metal member and metal member obtained by the same

ABSTRACT

A surface treatment method improves the surface properties of a metal member while maintaining the metal surface texture, and a metal member is obtained by the surface treatment method. The surface-treated metal member is obtained by bringing a solution of a fluorine-based polymer into contact with a surface of an anodic oxidation coating that is formed on a surface of a metal and has not been subjected to a sealing treatment, and subjecting the anodic oxidation coating to a steam sealing treatment, the surface-treated metal member comprising a fluorine-based polymer layer having a thickness of 100 nm or less, and a composite sealed layer that is formed continuously under the fluorine-based polymer layer, the composite sealed layer having a configuration in which the fluorine-based polymer is present inside pores formed in the anodic oxidation coating.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage Application of International Application No. PCT/JP2012/053635 filed on Feb. 16, 2012, and published in Japanese as WO 2012/111739 on Aug. 23, 2012. This application claims priority to Japanese Application No. 2011-033126 filed on Feb. 18, 2011. The disclosures of the above applications are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a surface treatment method for an anodizable metal member, and a metal member that is obtained by the surface treatment method and exhibits improved surface properties.

BACKGROUND ART

The surface of a metal member produced using aluminum, an aluminum alloy, magnesium, a magnesium alloy, titanium, a titanium alloy, or the like is generally provided with an anodic oxidation coating in order to improve corrosion resistance, design, and the like.

However, a metal member provided with only an anodic oxidation coating may exhibit insufficient corrosion resistance during long-term use.

A metal member provided with only an anodic oxidation coating may also be easily contaminated.

When a coloring step (e.g., secondary electrolytic coloring) is performed after anodizing, significant discoloration may occur due to insufficient corrosion resistance of the anodic oxidation coating.

In the fields of aluminum building materials and the like, a clear coating is provided after anodizing via anionic electrodeposition coating or the like in order to deal with the above problems.

However, since a clear coating has a thickness as large as 10 to 20 μm, the metal surface texture may be impaired.

Therefore, it is difficult to deal with the above problems by providing a clear coating when producing an automotive decorative member (e.g., decorative trim) for which the metal surface texture is important.

A transparent fluororesin coating that can provide corrosion resistance with a reduced thickness as compared with an acrylic clear coating or a urethane clear coating has been proposed.

JP-A-2006-257552 that aims at dealing with a wax remover discloses a technique that forms a polytetrafluoroethylene (PTFE) coating layer on the surface of an alumite coating.

However, since JP-A-2006-257552 states that it is appropriate that the thickness of the PTFE coating layer is 3 μm, a film-like surface texture is necessarily observed. Moreover, since JP-A-2006-257552 states that it is necessary to apply a primer or enlarge the pores formed in the anodic oxidation coating, the process is complex, and the treatment cost increases.

JP-A-2000-126680 discloses immersing a metal material provided with an anodic oxidation coating in a solution that contains a hydrophilic amorphous fluororesin so that the amorphous fluororesin enters the pores formed in the anodic oxidation coating. However, it is necessary to perform a preliminary heat treatment in order to improve the quality, and polymerize the fluororesin layer on the anodic oxidation coating by heating at 200° C. for 30 minutes.

Therefore, the coating layer disclosed in JP-A-2000-126680 has a large thickness, and a film-like surface texture is necessarily observed. Moreover, cracks may occur in the anodic oxidation coating when the anodic oxidation coating is heated at a high temperature of 200° C.

DISCLOSURE OF THE INVENTION Technical Problem

An object of the invention is to provide a surface treatment method that improves the surface properties of a metal member while maintaining the metal surface texture, and a metal member that is obtained by the surface treatment method.

Solution to Problem

According to one aspect of the invention, a surface-treated metal member that is obtained by bringing a solution of a fluorine-based polymer (hereinafter may be referred to as “fluorine-based polymer solution”) into contact with a surface of an anodic oxidation coating that is formed on a surface of a metal and has not been subjected to a sealing treatment, and subjecting the anodic oxidation coating to a steam sealing treatment,

the surface-treated metal member comprising:

a fluorine-based polymer layer having a thickness of 100 nm or less, and

a composite sealed layer that is formed continuously under the fluorine-based polymer layer,

wherein the composite sealed layer has a configuration in which the fluorine-based polymer is present inside pores formed in the anodic oxidation coating.

An electrolytic coloring step may be performed after forming the anodic oxidation coating as long as the fluorine-based polymer solution is brought into contact with the anodic oxidation coating that has not been subjected to a sealing treatment, and the anodic oxidation coating is then subjected to the steam sealing treatment.

According to another aspect of the invention, a surface treatment method for a metal member comprising:

forming a porous anodic oxidation coating on a surface of a metal, bringing a fluorine-based polymer solution into contact with the anodic oxidation coating in a state in which the anodic oxidation coating is unsealed or semi-sealed, and

subjecting the anodic oxidation coating to a steam sealing treatment.

The surface treatment method may further include subjecting the anodic oxidation coating to electrolytic coloring after forming the anodic oxidation coating, but before bringing the fluorine-based polymer solution into contact with the anodic oxidation coating.

The surface-treated metal member according to one aspect of the invention is characterized by including the composite sealed layer that is formed by subjecting the anodic oxidation coating to the steam sealing treatment in a state in which the fluorine-based polymer is present inside the pores formed in the anodic oxidation coating from the viewpoint of maintaining the metal surface texture. It suffices that the fluorine-based polymer layer that is formed continuously over the composite sealed layer have a small thickness.

The thickness of the fluorine-based polymer layer is adjusted to 100 nm or less, and preferably 10 nm or less, in order to prevent a situation in which the surface of the anodic oxidation coating has a film-like texture.

The aspects of the invention are applied to a metal member on which a porous anodic oxidation coating can be formed. The aspects of the invention are mainly applied to a metal member formed of aluminum, magnesium, titanium, or an alloy thereof.

The type of the anodic oxidation coating is not particularly limited as long as the anodic oxidation coating is porous. The metal member is anodized using a known electrolytic solution such as sulfuric acid or an organic acid.

The expression “has not been subjected to a sealing treatment” used herein in connection with the anodic oxidation coating means that the anodic oxidation coating has not been subjected to the steam sealing treatment, and means that the anodic oxidation coating may have been washed with water, washed with hot water, or semi-sealed using hot water at 60 to 90° C.

The anodic oxidation coating may have been washed with water, subjected to electrolytic coloring, and washed with water or hot water.

The term “electrolytic coloring” used herein refers to subjecting the anodic oxidation coating that has not been subjected to a sealing treatment to a DC electrolysis, AC electrolysis, or the like in an aqueous solution that includes metal ions (e.g., nickel ions or tin ions) to deposit the metal ions inside the pores formed in the anodic oxidation coating.

The term “steam sealing treatment” used herein refers to a sealing treatment that utilizes normal-pressure steam or pressurized steam.

The fluorine-based polymer used in connection with the aspects of the invention is a fluorine-based polymer that has such a molecular weight that the fluorine-based polymer can be dissolved in a solvent to prepare a solution.

Examples of the fluorine-based polymer include polytetrafluoroethylene, a polytetrafluoroethylene copolymer such as an ethylene-tetrafluoroethylene copolymer, polyvinyl fluoride, a copolymer thereof, polyvinylidene fluoride, a copolymer thereof, polychlorotrifluoroethylene, a copolymer thereof, and the like.

It is also effective to use a perfluoroalkyl group-containing fluorine-based polymer that is provided with water repellency and oil repellency and exhibits improved stain-proof properties.

Examples of the perfluoroalkyl group-containing fluorine-based polymer include a polyperfluoroalkyl (meth)acrylate, a poly(2-(perfluoroalkyl)ethyl (meth)acrylate), a tetrafluoroethylene-perfluoroalkyl vinyl ether, a poly(perfluoroalkyl vinyl ether), a poly(2-(perfluoro(alkyl)ethyl vinyl ether), and the like.

The perfluoroalkyl group is preferably represented by C_(n)F_(2n+1) (wherein n is an integer from 1 to 6).

The solvent used in connection with the aspects of the invention may be an organic solvent such as a ketone (e.g., acetone, MEK, or MIBK), ethyl acetate, butyl acetate, diethyl ether, dioxane, ethanol, or isopropyl alcohol. It is preferable to use a fluorine-based solvent that exhibits high affinity to the fluorine-based polymer.

The fluorine-based solvent also has an advantage in that it is unnecessary to use special ventilation/explosion-proof equipment.

Examples of the fluorine-based solvent include a perfluorocarbon, a hydrofluorocarbon, a hydrochlorofluorocarbon, a hydrofluoroether, a perfluoropolyether, a hydrofluoropolyether, and the like.

The fluorine-based polymer solution may be brought into contact with the anodic oxidation coating using an arbitrary means such as dipping, spraying, or brush coating.

ADVANTAGEOUS EFFECTS OF THE INVENTION

Since the surface-treated metal member according to one aspect of the invention includes the composite sealed layer in which the fluorine-based polymer is present inside the pores formed in the anodic oxidation coating, the surface-treated metal member exhibits excellent adhesion. Since the fluorine-based polymer layer that is formed continuously over the composite sealed layer has a thickness as small as 100 nm or less, the surface-treated metal member does not show a film-like texture.

Therefore, the surface-treated metal member exhibits excellent long-term corrosion resistance, is not easily contaminated, and can be easily cleaned by wiping the surface-treated metal member due to the water repellency and the oil repellency of the fluorine-based polymer.

When the surface-treated metal member has been subjected to electrolytic coloring, discoloration can be suppressed due to the improved corrosion resistance of the anodic oxidation coating.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows sample production conditions.

FIG. 2 shows evaluation results for samples.

FIG. 3 shows an SEM image.

FIG. 4 shows cross-sectional elemental analysis results.

FIG. 5 shows evaluation results for samples subjected to secondary electrolytic coloring.

FIG. 6 shows photographs of samples subjected to secondary electrolytic coloring after a salt spray test.

DESCRIPTION OF EMBODIMENTS

Metal member production examples according to several embodiments of the invention are described in detail below. Note that the invention is not limited to the following examples.

The surface of an extruded shape (T5 material) produced by extrusion using a JIS A 6063 alloy was subjected to a pretreatment (buffing and chemical polishing).

The extruded shape was anodized using a 15% sulfuric acid electrolytic solution at a current density of 1 A/dm² and a bath temperature of 20° C. to form an anodic oxidation coating having a thickness of 10 μm on the surface of the extruded shape (metal).

In Example 1, the anodic oxidation coating was washed with water. In Example 2, the anodic oxidation coating was subjected to a semi-sealing treatment (washing) at 80° C. for 10 minutes using purified water. In Examples 1 and 2, the anodic oxidation coating was then dipped in a fluorine-based polymer solution prepared by dissolving a fluorine-based polymer in a fluorine-based solvent (“OPC-800” manufactured by Noda Screen Co., Ltd.), and removed from the solution.

In Example 3, the fluorine-based polymer solution was sprayed onto the surface of the anodic oxidation coating.

The thickness of the fluorine-based polymer that adhered to the surface of the anodic oxidation coating removed from the fluorine-based polymer solution after dipping was estimated to be about 10 nm.

In Examples 1 to 3, the anodic oxidation coating was then subjected to a sealing treatment for 20 minutes using steam at 150° C.

Note that the steam sealing treatment may be performed under normal pressure. In this case, however, the sealing time may relatively increase. Therefore, it is preferable to perform the steam sealing treatment using pressurized steam at 130 to 180° C. (for 10 to 30 minutes).

In Comparative Example 1, the anodic oxidation coating was subjected to a boiling water sealing treatment at 100° C. for 20 minutes using purified water.

In Comparative Example 2, a fluororesin primer was applied to the anodic oxidation coating subjected to a boiling water sealing treatment in the same manner as in Comparative Example 1, and the anodic oxidation coating was then dipped in the fluorine-based polymer solution, and dried.

In Comparative Example 3, the anodic oxidation coating was treated, and dipped in the fluorine-based polymer solution in the same manner as in Example 2, but was then dried without subjecting the anodic oxidation coating to the steam sealing treatment.

In Comparative Example 4, the anodic oxidation coating was treated, and dipped in the fluorine-based polymer solution in the same manner as in Example 2, but was then subjected to a boiling water sealing treatment at 100° C. for 20 minutes using purified water.

The external appearance of the samples obtained in Examples 1 to 3 and Comparative Examples 1 to 4 was evaluated with the naked eye. The samples were then subjected to a 200 hr salt spray test, and the color difference due to the test was measured (chroma meter: “CR-400” manufactured by KONICA MINOLTA INC.).

FIG. 1 shows the sample production conditions, and FIG. 2 shows the evaluation results.

Note that “DIP” in FIG. 1 refers to “dipping”.

As shown in FIG. 2, the samples obtained in Examples 1 to 3 maintained their metal surface texture, and did not show a change in surface quality due to the salt spray test.

In contrast, the sample obtained in Comparative Example 1 showed slight surface whitening, and the sample obtained in Comparative Example 2 showed a trace of the primer, and had an inferior texture.

The sample obtained in Comparative Example 3 was not subjected to the steam sealing treatment after dipping the anodic oxidation coating in the fluorine-based polymer solution. As a result, the sample obtained in Comparative Example 3 showed whitening (discoloration) when subjected to the salt spray test.

The sample obtained in Comparative Example 4 was subjected to the boiling water sealing treatment after dipping the anodic oxidation coating in the fluorine-based polymer solution. As a result, the sample obtained in Comparative Example 4 showed slight surface whitening.

It was thus confirmed that it is insufficient to merely dip the anodic oxidation coating in the fluorine-based polymer solution, or spray the fluorine-based polymer solution onto the anodic oxidation coating, and it is effective to perform the steam sealing treatment after dipping the anodic oxidation coating in the fluorine-based polymer solution, or spraying the fluorine-based polymer solution onto the anodic oxidation coating.

The cross section of the sample obtained in Example 2 was observed using a scanning electron microscope (SEM), and the elements were semi-quantitatively analyzed.

The results are shown in FIGS. 3 and 4.

A scanning electron microscope “JSM-7000FZ” (manufactured by JEOL Ltd.) was used for cross-sectional observation, and an EDS analyzer “EX-2300xBU” (manufactured by JEOL Ltd.) was used for semi-quantitative elemental analysis.

FIG. 3 shows the resulting SEM photograph.

FIG. 4 shows the elemental analysis results for the surface, the upper part of the cross section, and the lower part of the cross section (see FIG. 3).

The thickness of the fluorine-based polymer layer formed on the surface could not be measured since the thickness of the fluorine-based polymer layer was very small. Since fluorine was detected (deposited) in the upper part of the cross section of the anodic oxidation coating, it was confirmed that a composite sealed layer was formed in which fluorine was present inside the pores formed in the anodic oxidation coating.

In order to check the effects of electrolytic coloring, a sample of Example 4 was obtained in the same manner as in Example 1, and subjected to the salt spray test, except that the anodic oxidation coating was washed with water, and subjected to secondary electrolytic coloring (black) using a nickel-tin mixed bath.

In Comparative Example 5, the anodic oxidation coating was subjected to secondary electrolytic coloring in the same manner as in Example 4, and then subjected to the boiling water sealing treatment in the same manner as in Comparative Example 1 without bringing the fluorine-based polymer solution into contact with the anodic oxidation coating.

FIG. 5 shows the measurement results for the color difference due to the salt spray test.

FIG. 6 shows photographs of the samples obtained in Example 4 and Comparative Example 5 after the salt spray test.

It was thus confirmed that the anodic oxidation coating subjected to secondary electrolytic coloring maintained its metal surface texture, and exhibited improved corrosion resistance as a result of forming the fluorine-based polymer layer on the anodic oxidation coating, and subjecting the anodic oxidation coating to the steam sealing treatment.

INDUSTRIAL APPLICABILITY

The surface treatment method according to the embodiments of the invention is suitable for a metal member on which a porous anodic oxidation coating can be formed, and may be applied to various fields (e.g., automotive parts) that utilize such a metal member. 

1. A surface-treated metal member that is obtained by bringing a solution of a fluorine-based polymer into contact with a surface of an anodic oxidation coating that is formed on a surface of a metal and has not been subjected to a sealing treatment, and subjecting the anodic oxidation coating to a steam sealing treatment, the surface-treated metal member comprising: a fluorine-based polymer layer having a thickness of 100 nm or less; and a composite sealed layer that is formed continuously under the fluorine-based polymer layer, wherein the composite sealed layer has a configuration in which the fluorine-based polymer is present inside pores formed in the anodic oxidation coating.
 2. The surface-treated metal member as defined in claim 1, wherein the anodic oxidation coating that has not been subjected to a sealing treatment has been subjected to electrolytic coloring.
 3. A surface treatment method for a metal member comprising: forming a porous anodic oxidation coating on a surface of a metal; bringing a fluorine-based polymer solution into contact with the anodic oxidation coating in a state in which the anodic oxidation coating is unsealed or semi-sealed; and subjecting the anodic oxidation coating to a steam sealing treatment.
 4. The surface treatment method as defined in claim 3, further comprising: subjecting the anodic oxidation coating to electrolytic coloring after forming the porous anodic oxidation coating, but before bringing the fluorine-based polymer solution into contact with the anodic oxidation coating. 